Service observation system



Oct. 15, 1935. L. H. ALLEN E'rAL 2,017,644

SERVICE OBSERVATION SYSTEM Filed Jan. 6, 1933 9 Sheets-Sheet 1 MARC/N41.

ATTORNEY POLAR/ZED l I /.9

Oct. 15, 1935. 1 ALLEN ET'AL 2,017,644

SERVICE OBSERVATION SYSTEM Filed Jan. 6, 1935 9 Sheets-Sheet 2 FOLAR/ZED L. H. ALLEN //vv/v TORSR MASSONNEAU ATTORNEY Oct. 15, 1935. ALLEN ET AL 2,017,644

SERVICE OBSERVATION SYSTEM Fi led Jan. 6, 1953 9 Sheets-Sheet 3 L .H. ALLEN INVENTORS R. E MASSO/VNEAU ATTQRNEV Oct. 15, 1935. H. ALLEN ET AL SERVICE OBSE RVATION SYSTEM Filed Jan. 6, 1935 9 Sheets-Sheet 4 x at INVENTORS ALLEN RE MASSONNEAU Qaw ATTORNEY Oct. 15, 1935. L. H. ALLEN ET AL SERVICE OBSERVATION SYSTEM Filed Jan. 6, 1953 9 SheetsSheet 5 .I l I l I l l Q5 r. nHu E \R L. H. ALLEN T Assm/gaw IN VEN TOPS Oct. 15, 1935. 1+, ALLEN ET AL 2,017,644

SERVICE OBSERVATION SYSTEM Filed Jan. 6, 1935 9 Sheets-Sheet 6 LAST 105.

ST TRUN y L../-/ ALLEN u. M Q R. F.MA$SONNAU ATTORNEY FIRE T TRUNK SERVICE OBSERVATION SYSTEM Filed Jan; e, 1953 9 Sheets-Sheet 7 SECOND 77PUNK k I ll 9 L. h. ALLEN 'NVENTORS RJ-T- MASSONNEAU 9am Arl'bewr Oct 1935'. L. H. ALLEN ET AL 2,0'l7,6 SERVICE OBSERVATION SYSTEM Filed Jan. 6, 1955 9 Sheets-Sheets L. H ALLEN WVNTORSRMA$$0NNAU By $13M 1 AT7UQNEY 1 1935- 1.. H. ALLEN El AL 2 ,017,6 v SERVICE OBSERVATION SYSTEM I Filed Jan. 6, 1933 9 Sheets-Sheet 9 r 1.. ALLEN NT /a EMSSQN/VEAU f mam .7

ATZIORNEY.

Patented Oct. 15, 1935 UNE SERVICE OBSERVATION SYSTEM Application January 6, 1933, Serial No. 650,474

22 Claims.

This invention relates to telephone exchange systems and is more particularly concerned with what is known as centralized service observation equipment, that is, apparatus for studying from a central point the quality of service given on a particular subscribers line.

In such systems, where machine switching apparatus is employed at the central office for setting up connections, it sometimes happens that a subscriber will complain of poor service. The substance of these complaints embraces almost the entire range of telephone service and necessarily includes such items as wrong numbers, dont answer calls, overcharges and the like any or all of which may be either due to the improper use of the calling device or the faulty performance of the central office equipment. It becomes necessary, therefore, when a subscriber complains of poor service, to determine from an actual observation of his line whether poor service is actually being rendered and, if so, to determine the cause.

There are two ways of doing this. One is to provide at the local office a special observation desk equipped with apparatus and circuits for taking all the required observation on subscribers lines. The observation operator presiding over the desk, in such a case, may inspect the operation of all switching equipment involved in the particular subscribers line responsive to the origination of a call thereon. The other is to provide switching facilities at the local ofiice in which subscribers lines are located and by which the lines to be observed are connected over a common trunk to a, central observing point. The operator located thereat can then observe, monitor or supervise, the service on groups of trunk lines extending to a plurality of outlying ofiices or exchanges and to which trunk lines are connected the subscribers lines under observation.

Our invention has to do with the latter of the two methods and is particularly concerned with a. central observing bureau provided with a plurality of service observation desks at each of which are extended the trunks connecting with the several .outlying offices.

tion desk only if said desk is occupied and idle;-

the signal being advanced to the next preferential desk if the previous one is either busy or unoccupied.

Another novel feature of our invention is concerned with the transmission of a group of impulses to the service observation desk at which a call is taken up for observation to designate the numerical indication'of an arbitrary number assigned to the line making the call from a particular local office so that the central operator, in observing the service on said line over a trunk in that oihce, may identify the line connected thereto by its numerical designation.

Yet another feature of our invention is com cerned with the means provided at the central observing bureau whereby an operator may both talk and listen either to the subscriber Whose line is under observation or to any one of the maintenance force in the oifice with which the central observation desk is then operatively connected over an observing trunk line.

Yet another feature of our invention has to do with an arrangement between calling observing lines, the observing trunk and the observation position whereby a calling line may not be connected to the observation trunk if, prior to the initiation of a call, said trunk has not been locked into said position through the occupation thereof, thereby insuring service observation on said line from the very inception of the call.

In accordance with the invention, therefore, one specific embodiment of which is disclosed herein by way of illustration this is accomplished in the following improved manner: At the local office the group of lines to be observed at the central bureau is connected to circuit control devices for extending one of such lines when calling over a trunk connecting said oflice with the central service observation bureau. A group of registers is associated with the connecting trunk to which each of said lines is cross-connected in accordance with an arbitrary number assigned for identification purposes.

The connecting trunk contains the usual sensitive and amplifying devices of the type disclosed in Patent 1,795,656 to R. F. Massonneau, granted March 10, 1931 but in addition thereto, an impulse circuit is provided which cooperates at the proper time with the above mentioned registers to transmit a group of impulses characteristic of the arbitrary identifying number assigned to a line to be observed.

The service observation connecting trunks radiate from the central service observation bureau to all of the local offices embraced in the service observation area and each of these trunks is multiplied to all the observation desks at the bureau. A preference lock-out arrangement associates together at each desk all the trunks from the various ofiices, and the taking up of a trunk from any oflice at a preferred desk automatically advances the preference of a succeeding call from any oifice to the next succeeding idle desk.

Each desk is provided with an appropriate impulse responsive device and a lamp display indicator controlled thereby both of which, at the proper time, become associated with the trunk which has been locked into the position. The group of impulses designating the number assigned at the local ofiice to the calling line is received by said responsive device for setting said indicator to display at the position the identifying number of the line under observation.

When, therefore, a subscribers line which is marked for observation, initiates a call the line is automatically connected to the trunk extending to the central observation bureau. The preference lock-out circuit operates to extend the connection to the first preferred desk which is both idle and occupied and a lamp associated with the trunk is lighted to indicate the appropriation of the trunk for service observation purposes. Immediately thereafter, that is, after the trunk has been locked into position, the impulse circuit at the local ofiice is operated in conjunction with the operated registers and impulse circuit to transmit to the operators position the group of impulses which identify the assigned number of the calling line under observation.

The observation desk is provided with appropriate equipment to supervise all the functions necessary in the setting up of a call, the operator listening to the various impulses and signals transmitted over the subscribers line to set up the call while a pen register records said impulses and signals. The operator is further provided with means for fully controlling the disposition of the subscribers line and may talk to the subscriber or to a maintenance man in the connecting office if desired. When the operator is satisfied with the observations -on the line or is otherwise satisfied that all possible action has been taken thereon, said line may be either further held or disconnected in which latter event the trunk is returned to normal, the indicator is extinguished and the desk cleared for other incoming service.

A clearer conception of the scope and purpose of the invention may be obtained from a consideration of the following description and attached drawings in which:

Fig. 1 shows a subscribers line connected to an outgoing service observation trunk equipped with parallel extension circuits to a plurality of other lines;

Figs. 2 to 5, inclusive, show the outgoing equipment and cooperating circuits of said outgoing service observation trunk;

Figs. 6 and '7 show a number of incoming service observation trunks from different local service observing offices including the trunk shown in Figs. 2 to from the central o-fiice of Fig. 1. These trunks terminate in a plurality of central observation positions, the circuit equipment of one of which is shown in detail in Figs. 6, 8, and 9;

Fig. 8 shows the observing line number indicating circuit furnished for each central observation position; and

Fig. shows how Figs. 1 to 9 are to be arranged with respect to each other in order to disclose the invention completely.

The subscribers line A, which is one of a plurality of lines terminating in the contacts of 5 the line finder I I 6, in entering the central office, is first connected to the main distributing frame MDF. From here it is extended to the terminal racks of the intermediate distributing frame IDF. At said intermediate distributing frame, the line 10 is connected to the desired terminals in the bank of the line finder frame H6. When, however, it is desired to make observations on the subscribers line A a shoe I I5 is attached to the line side of intermediate distributing frame. This shoe is the terminating end of a pair of cords I00 and IGI. To complete the association of the line A with the outgoing trunk extending to the central observing bureau, the plugs of said cords are inserted, respectively, in the jacks I02 and I03 in which the observation trunk terminates, provided at some convenient location in the vicinity of the distributing frame. In this manner, the line A is connected by means of a special trunk to the plurality of central observation positions, which trunk extends to each one of said positions as shown in Fig. '7.

In a like manner any desired number of other lines, similar to line A, may be extended to the central observation positions over the same outgoing trunk through parallel connection extensions thereto by means of other connecting shoes and cords plugged into trunk multiple jacks such as II? and II 8. The number of jacks multipled to each trunk depends on the number of lines which are to be observed over a given period of time. For the purpose of this description, it is assumed that a maximum of 100 lines may be connected to the special service trunk, and that line A comprises one of the lines in 4,0 such an observing group. It is further assumed that line A, for purposes of identification, is given the arbitrary number I1.

Assuming, therefore, that line A is connected to the service observation trunk through jacks 4,5 I02, I03, as described, then, when the subscriber removes his receiver from the switchhook a circuit is completed from ground on the right contacts of cut-off relay I20, tip conductor I22 of the subscribers loop, ring conductor I23 of the subscribers loop, left inner contacts of relay I20, winding of relay I2I to battery and, in parallel thereto, ring of cord plug I00, sleeve of jack I02, contacts of relay I05, winding of relay I04 to battery. Both relays I2I and I04 operate, the former to close circuits for starting a line finder switch in motion for connection with the terminals of the calling line on the line finder frame I I6 and the latter to initiate operations for extending the service observing trunk to an idle 0 and occupied observing position at the central observation bureau.

The operation of relay I04 closes a partial path from battery on the back contacts of relay 505,

conductor I08, lower winding of relay I01, back 5 contact of relay I06, contacts of relay I04, conductor 405, to the right back contacts of relay Bill. Now if the trunk is in a condition to accept the call; that is, if an operator is servicing any one of the observing positions atthe central ob- 7 servation bureau to which the trunk has access, relay 6M may or may not be operated depending on whether or not the position has become occupied prior to the initiation of the call by the calling line under observation. 15

Now, a position at the central observation bureau is made responsive to the seizure of a trunk terminating thereat by the operator plugging her telephone headset into the telephone jacks 900 located at that position. When this takes place, a circuit is closed for relay 90I extending from ground on the make-contacts of the monitoring jacks 900 to the winding of said relay causing said relay to operate. Relay 90I, over its left inner contacts, connects ground to conductor 903 and causes the operation thereby of relay BOI over a path extending from ground on conductor 903, left normal contacts of relay 904, conductor 905, left inner normal contacts of relay I of the first trunk of all service observing trunks incoming from outlying offices and capable of connection to said position, left inner normal contacts of relay 'IOI of the second trunk, similar contacts of similar relays of all other trunks, including the left inner normal contacts of relay 600 of the last trunk, conductor I02, winding of relay 50I to battery, and. in parallel therewith, through the winding of relay 602 to battery causing both of these relays to operate. Another circuit is closed from battery through the winding of relay I53, conductor I09, right inner contacts of relay 002, conductor 902, to ground on the left outer contacts of relay 90!. Relay I03 operates. By the operation of relay I03 ground is connected to conductor 434 of the first observation trunk of Fig. '7 from ground on the left contacts of trunk key I05, left outer contacts of relay I03, left outer normal contacts of relays I09",'I0'I', I08, there being one such i relay for each position to which the trunk is connectible, to conductor 434. Similar circuits, controlled by relay I03, connect ground to conductors corresponding to conductor 434 of other trunks. This ground closure in each idle trunk further extends over the respective trunks to the local ofiices from which the trunks extend and. there complete a circuit, for example, over the left back contact of relay 50I, winding of relay 500 to battery. Relay 500 operates and closes a circuit extending from ground over its contacts, conductor 502, right inner back contacts of relay 300, conductor 506, left back contacts of relay 503, winding of relay 400 to battery. Relay 400 operates and closes an obvious circuit through the right winding of relay 40I which also operates. If, now, relay 49I becomes operated during the time that the set-up of a call is already in progress such as that of line A above described. the path extending from battery on the back contacts of relay 505 to the right armature of relay 40I will now be completed in a circuit over the right front contacts of relay 40I, winding of relay 403 toground. Relay 493 operates and closes a locking path to the left winding of relay 4! to hold it operated after relay 400 releases which it subsequently does as explained hereinafter. Relay I0! is now in series with relay 403 in the above described circuit and does not operate since it is marginal. Nothing further happens until the line finder whose movement was started by the operation of relay I2I succeeds in connecting with the terminals of the line H6 in the Well known manner whereupon a circuit is completed from a ground source in said line finder, second brush and terminal from the bottom on line finder frame H6, right winding of relay I20, to battery, and in parallel therewith over the tip of shoe cord ml and tip of the trunk jack I03, winding of relay I95, to battery. Relay I20 operates and opens the circuit of the line relay I2I and relay I operates and opens the above traced circuit of relays 403 and M1. Since relay I01 was not operated but only relay 403, relay 403 releases, in turn releasing relay 40L Since relay I05 remains operated for the entire duration of the call, line A can not become connected to the service observation trunk for any observations on that call. Hence, if an operator happens to make the position available after a call has been started and before the line finder has found the calling line, the operation of relays 403 and 40! looks out the line from any possible connection with the service observation trunk since itis not desirable to make observations on any line unless such observations can be made from the very inception of the call.

The same thing is true regardless of whether one line or all the lines of the line group initiate calls just before the operator makes the position available. For, in this case, the circuit of relay 403 is paralleled through the winding of each relay I01 of the separate extension circuits to each of which the separate lines of the group are extended but none of which relays can operate since each one of them is marginal. As each line is found by a line finder circuit, each of the parallel paths to relay 403 is opened by the release of relay I04 in each of the extension circuits, relay 403 and hence relay 40I, releasing when the circuit of the last line to be locked out is opened by the release of relay I04 of its extension circuit.

When, however, the operator makes the position available at a time when none of the lines are calling, relays 400 and MI operate as already described. A circuit is now closed from battery through the winding of relay 503, right outer back contact of relay 504, conductor 402, left inner front contacts of relay 40I, to ground on the contacts of relay 500. Relay 503 operates, locks over a circuit through the right outer contacts of relay 594, left front contacts of relay 503, conductor 506, right inner back contacts of relay 300, conductor 502, to ground through the contacts of relay 590. Relay 503, by opening its back contacts, opens the circuit of relay 400 which now releases and causes the release of relay 40! unless at the termination of this preliminary test, a line has initiated a call and closed the circuit for relay 403 which then holds relay 40! looked over its left winding after relay 400 releases as above described. If,-however, no line circuit has initiated a call during the time when relay 40! is operated, said relay will release after the preliminary test. With relays 503 operated, the trunk is in a receptive condition to lock in an observing line for the purposes of service observation. On the other hand, if no position is occupied, relay 400 does not operate. relay 593 does not operate in which event the trunk is in a non-responsive condition and can be made so only through the operation of the preliminary test described above.

It is also evident from the operations so far described that while the circuit of relay 400 is not closed through if no position is occupied, the same condition must likewise prevail if all positions are occupied and busy. For, if each position is busy, it will be shown hereinafter that the circuit of relay I03 becomes opened when the last position becomes occupied and busy and ground, therefore, is not available on conductor 434 and relay 400 can not operate.

Assuming now, that the above preliminary test has been made and relays 500 and 503 operated,

the trunk circuit is now prepared to lock in the calling line on which a call is originated thereby resulting in the operations of relay I 04 and relay I05 as already described, and further operates to extend said line over the trunk line to an occupied operators position at the central observation bureau.

With relay 503 operated, ground on its front contacts is extended through the right back contacts of relay 40L conductor 404, and over the previously described circuit including the lower winding of relay I01 and battery on the back contacts of relay 505. Relay M1, being marginal, did not operate at the time it was included in the circuit of relay 403 as already described. But when relay 40I released, ground from the right contacts of relay 503 was connected to conductor 404 and the winding of relay 403 eliminated from the circuit of relay I01 so that said relay now operates and locks over its top winding and top inner contacts, conductor I09, winding of relay 505, to

' ground on the left outer back contacts of relay 4!) I.

Relays I06 and 505 now operate through the locking contacts of relay I 01. Relay I06 opens the operating circuit of relay I01 over its left inner contacts and causes the ground on conductor 404 to be thereby extended through the bottom'inner contacts of relay I01 to conductor H0, right contacts of relay 405, winding of relay 406 to battery, operating relay 406, while over its top and bottom outer contacts, respectively, relay i? further extends the calling line over conductors III and H2 of the trunk to the input terminals of the monitoring amplifier 4 I 0. Relay 406 operates and locks in series with the winding of relay 405, left contacts of relay 406, conductor 422 to ground on the left outer contacts of relay 504, which last mentioned relay operated over an obvious circuit when relay 505 operated. Relay 405, however, remains short circui-ted by said locking ground and said ground over H0. The operation of relay 400 connects battery through resistance 401 over its right contacts to the tertiary winding T of the polarized relay 408 to place this relay on its back contact and partially prepares a circuit for later locking relays 400 and 405 in series.

Relay 505 operated, disconnects battery from conductor I08 so that no other calling line can be locked in as long as relay 505 remains operated. Relay 505 further connects battery through its left front contacts, resistance 4 and normal contacts of relay 4I2, lower winding of retardation coil 413 to conductor 4 I4 of the trunk extending to the central observing bureau. Relay 505 also connects ground over its right outer contacts, resistance 4l5, normal contacts of relay M6, top winding of retardation coil M3 to conductor 4I1 of said trunk.

The connection of battery and ground through retardation coil M3 to the trunk extending to the centralobserving bureau completes the circuit of polarized relay 104 bridged across said trunk conductors 4 I 4 and 4 I 1. Relay 104 operates and connects ground on its front contacts over the right contacts of key 105, to the chain path which is looped through the left outer back contacts of all relays 100 of the particular trunk. This ground will then seek battery over a circuit path to the winding of a relay 100 of the position occupied, as is evidenced by the operation of relay 00L For example, if the position occupiedhappens to be the one marked by relay 60I that is, the positiona1 circuit shown in Figs. 6, 8, and 9 and, besides,

; all other positions are vacant, then the circuit will be completed from ground on right contacts of key 105, left back contacts of relays 100, 100,100", conductor 106, right outer contacts of relay 60I, conductor 803, winding of relay 100 to battery, operating relay 100. On the other hand, if more than one position is in a receptive condition, say the positions identified by marking relays BOI, 69I', and00l", all of which relays would be operated, then the ground on conductor 106 would form a plurality of parallel paths over the right outer contacts of relays 60I, GUI and BM" re- 10' spectively, to the windings of relays 100, 100', and 100" respectively, tending to cause all of these relays to operate. The operation of any one of them, however, say relay 100, opens the left back contacts of said relay and through which the chain circuit to the other relay 100 and 100" is extended. The opening of the chain opens the circuit to each of the'relays 100 and 100" so that these relays either do not operate or are released when relay 100 looks through its left inner front 20.

contact, conductor 905, left normal contacts of relay 904 of the position circuit locked in with the trunk, conductor 903, to ground on the right inner front contacts of relay 901.

Should the trunk so connected with a calling 26.

trunk or relays 600, SUM-600" of the last trunk.

If the trunk taken into use is the second one and relay 10I is operated, then the locking circuit of this relay extends from its left inner contacts over the left back contacts of relay 100 to ground on conductor 905 as previously described. 85

In case two or more trunks are simultaneously taken by calling lines at their respective central ofiices and there is but one observation position available at the central observation bureau, then the relay corresponding to relay 100 of each trunk 40- will operate over separate circuits like the one above traced. However, since the locking circuit of each of these relays is controlled over a chain circuit extending over back contacts of all trunk relays of preceding trunks, the preferred trunk at the beginning of the chain will open the locking circuit of the later and less preferred trunks. If, for example, the second and the last trunks are simultaneously taken and the position marked by the operation of relay GM is the only one available, then the trunk relays 000 and 10 I are both operated. But since the trunk of which relay 10I forms a part is first in the locking chain preference, the operation of relay 10I opens the locking path to conductor 905 for other trunk relays having later preference, whereupon relay 800 releases.

If, however, there is more than one position available, the observation trunk which was locked out of the first position will be transferred to the next preferred position available or, if only one other position is available, then it is transferred to that position. This is accomplished as follows: Assuming the trunks taken into service to be the first and last, then, when relay 100 operates it opens the-circuit of relays MI and 602. Relay v 602 releasing, closes a circuit for operating relay 906 extending from battery through the left back contacts of relay 602, winding of relay 906 to ground on conductor 903. The operation of relay 906 extends battery from the contacts of relay 002, front contacts of relay 9% to the winding of relay 002 of the next position. If that position is occupied then the circuit of relays 60 l and 602 is completed in the same manner as was that of relays GM and 602. With the operationof these Tb relays and the failure of trunk relay 600 to lock into the first position and the consequent opening of its circuit by the release of relay 60 I, a circuit is now completed from ground at the front contacts of relay 604, right contacts of key 505, left back contacts of relays 600, 600-600, right inner contacts of relay 703, conductor 606, right inner contacts of relay 50!, winding of relay 600' to battery. Relay 600' operates, locks to ground on conductor 903 of the position marked by relay 602 .and performs the same functions with respect to future operations as is peri ormedby relay 100 of the trunk assumed to have been locked in the first position.

It will be noted that the battery supply for relay 602 of the first position is connected permanently to the winding of this relay while that of relay 602' of the next position is furnished either from the back contacts of relay 90! or from the back contact of relay 602 and both through the front contact of relay 906, all of said relays being in the first position. Therefore, if the first position is occupied and relays 90! and 602 operate in consequence, as already described, any trunk taken for observation service by .a calling line is locked in the first position even though the second position may also be occupied at the same time because, until a trunk with .a calling line locked thereto is connected to the first position, there is no way of extending battery from this position to thewinding of the marking relay of the next position even though said next position is occupied. Since, however, the occupation of the second position is ineffective until relay 602' is operated, and since this relay cannot operate because its battery is cut ofi at the preceding position by the opening of the back contacts of relays 602 and 90!, the only possibility of a trunk being locked into the second position is by furnishing a battery supply for relay 602 through the back contacts of relay 602 and the front contacts of relay 906 as already described. This event, however, occurs only when a trunk has been locked into the first position as is evidenced by the release of relay 602 and the operation of 906 at which time the previously traced battery supply is connected to the winding of relay 602. That is to say, the service observation trunks are locked into the observing positions at the central observing bureau in a definite preferred order and a trunk is not switched from one position to the next until the previous positions are all busy with trunks locked in with respective calling lines connected thereto.

Should the first position be unoccupied and the second position occupied, then the service observation trunk will be locked in to the second position, for, in this case, the fact that the first position is unoccupied causes relay 901 to be normal, in which event battery through its back contact is connected directly to relay 002 of the second position which relay then operates in the same manner as relay 602 operated at the time the operator at the second position plugged her telephone headset into the position jack of her position.

It is to be further observed that there is no restriction on the number of trunks which can thus be used compared-to the number of available positions, except that the number of simultaneous observations possible is limited, of course, to the number of positions. When all positions are busy, therefore, all trunks which are not in use are immediately placed in an unresponsive condition so that any calling line in the group marked for observation at the local oifice to which each of the trunks extends will not be locked to the trunk. It will be recalled that the signal for trunk responsiveness is a ground on conductor 434 which eventually re- =7 common to all the service observation trunks,.

there being one pair of contacts for each of said trunks on said relay. The circuit of relay 103, however, is paralleled to the right inner contacts of relay 602, 602'-602" and is completed by relay 602 of the first position over conductor 902 which is grounded as -soon as the first position is occupied and is further provided with a by-path over the back contacts of relay 906 to ground over conductor 903. Consequently, when the first position is occupied r-elay 103 is operated over the front contacts of relay 602 as already described. Relay 602, however, releases when the position is locked to the trunk so that one of the operating paths for relay 103 is opened. Further, when relay 906 operates for the purpose of transferring operating battery to relay 602' of the next position, another path for holding relay 103 is opened. However, the operation of relay 602' in the next position closes another circuit to hold relay 103 to ground on conductor 902 of that position. And when this position becomes busy, by being lockedin with a trunk, the holding circuit for relay 103 is advanced to relay 602" of the next position until finally, the last position is reached at which time, as soon as the position becomes busy and relay 602" is released and relay 906 operated, the last holding circuit of relay 103 will have been opened. Relay I03 releases and, so long as all positions are occupied and busy, relay 103 cannot thereafter operate. Since, however, conductor 434 of each trunk is connected to one of a pair of contacts on relay I03 and since, further, the responsive ground signal over a trunk conductor 434 is possible only if relay 103 is operated it is evident that if all positions are busy, the remaining idle trunks are left in an unresponsive condition thereby avoiding the connection of any calling lines thereto.

Referring to the operation of the first trunk locked into the position marked by relay 602, the operation of relay 100, lights the trunk lamp 101 at the position to identify the trunk to which a calling line has been locked. It further closes an obvious circuit for relay 108 which operates and closes through the trunk conductors 433, 434, M1, and M4 to the equipment of the service observing operator in preparation for observing subscriber dial impulses.

Relay 108 further closes a circuit for relay 908 extending from ground on its right inner contacts, conductor 935, right normal contacts of relay 904, winding of relay 908 to battery. Relay 908 operates and, by opening its left outer contacts, removes the shunt around the operators receiver (not shown) after condenser 909 has been connected through to talking conductor 414 by way of conductor 936, thereby preventing any possible click to the operator during the initial surge of current into the condenser. Relay 908 is slow to operate in order to provide means for.

discharging the trunk cable prior to connecting impulse responding relays, to be described hereinafter, to the trunk conductors thuseliminatlng relay 42 I.

the possibility of falsely operating any of said relays.

In the meanwhile the operation of relay 504 closes the locking ground for relay 406 as above described. Relay 504 further connects supplementary ground to conductor 404 from its left inner contacts, right back contacts of relay 40!, and at its right outer contacts, opens the circuit of'relay 503 which releases after an interval. Relays 406 and 405 are placed under the control of relay 504 to insure their operation in those cases where the terminals of the calling line on the line finder frame are at the bottom of the line finder contact bank in which case the line finder hunting time is small. With the connection of the line finder to the terminals of the calling line and the cut-off relay I20 operated in the well known manner, the circuit of relay I04 is opened as already described and ground is re- 4 moved from conductor H; If the travelling time of the line finder elevator is very small, ground over conductor H0 may not be on for a sufliciently long time to operate relay 406 and the consequent operation in series with it of relay 405 when the calling line is found by the line finder and relay I04 releases. Consequently, when relay 504 operates and relay 406 has not yet operated, it is operated by the supplementary path above described except that, in this case, relay 405 is operated in series with it since the absence of ground in conductor H0 indicates the line to have been found and, therefore, no longer necessary to keep relay 405 short circuited. Relay 405 operated connects the winding of relay 420 over its front contacts and right back contacts of relay 42I to conductor H2 of the line by way of normal contacts of key 422, and opens the original path of relay 406.

As soon as the subscribers line locked to the observation trunk becomes associated with a register sender or first selector in the known manner, relay 420 operates in parallel with the pulsing relay of the sender in a circuit completed from ground through said relay, over conductor H2, bottom outer contacts of relay I01, sleeve of trunk jack I 02, ring of connecting cord I 00, second from the top terminal and associated brush of connecting line finder H0 winding of said relay in the sender to battery. Relay 420 operates and closes an obvious circuit for operating Relay 42I operates, locks to ground on conductor 422, disconnects relay 420 from conductor II 2' of the line which relay then releases, and further connects ground from the right inner contacts of relay'505 to the armature of relay 408.

The observation trunk circuit as well as the operators position to which the trunk is locked, are now ready to respond to the next operations of the subscribers line under observation which will generally be that of dialing the called subscribers number. Before describing pulsing operations, however, it is desirable to proceed with that portion of our description which has to do with the identification to the service observer of the arbitrary line member assigned to the line on which observations are to be made.

'At the time a calling line is to be supervised and is, therefore, connected to the trunk extending to the central observing bureau. by the connection cord-shoe I I as already described, the line itself is assigned an arbitrary numerical designation as one of a group of one hundred lines. Conductor I I3 of the line extension circuit is cross connected to one of ten terminals TO9 on the cross connecting block 230 depending on the tens digit of said arbitrary designation, while conductor H4 is cross connected to one of ten terminals U0-9 of said block depending on the units digit of said arbitrary designation. Re-

lays 200 to 203, inclusive, operate through their primary windings (P) for the tens digit 1 to 4 respectively, relay 204 operating alone for the tens digit 5. For the digits 6 to 9 inclusive, relays 200, 20I, 202 or 203 respectively operate through their secondary windings (S) in series with the winding of relay 204. For the tens digit 0, battery is supplied through resistance 205. The unit digit registration is made through the operation of relays 2I0 to 2I4, inclusive, and in a similar manner to that described for the tens digit except that ground instead of battery is supplied to the windings of these relays as more completely described hereinafter.

When relay I06 operates as already described and conductors H3 and H4 are joined at the right contacts of said relay, one of the relays in the tens group is operated in series with one of the relays in the units group. As an example, it has been assumed that the arbitrary designation number assigned to calling line A is IT and conductor H3 of the extension circuit connecting with said line is connected to terminal T-I and conductor H4 to U-l. Upon the operation of relay I06 and the consequent joining of conductors H3 and H4, a circuit is closed from battery through the primary winding P of relay 200, terminal T-I, conductor H3, contacts of relay I06, conductor H4, terminal U--'I, secondary winding S of relay 2| I, winding of relay 2I4, conductor 2| 6, left outer back contacts of relay 300, conductor 422 to ground on the left outer front contact of relay 504. 2I2, and 2M operate. Relay 200 connects battery through high resistance 2I'I to the left inner contacts of relay 302. Relay 2H prepares a partial path through low resistance 2I8 to the left outer front contact of relay 304, while relay 2 I4 performs no useful function at this time.

Now the arbitrary designation I1 is to be transmitted to the central observation position to which the trunk is locked so that the operator thereat may note such designation and thereby identify the line which is being observed. This indication is transmitted in the form of a pulse code of the kind commonly used in automatic telephone systems to transmit called line designations. It comprises a code of four impulses for each digit, two of which are of either light or heavy negative polarity and the other two of which are either positive or no polarity. For a further description of an impulse code of this kind, reference is made to Patent 1,844,147 to E. H. Clark, dated February 9, 1932.

When, therefore, the trunk is locked into a position and relay 504 operates as before described, the ground on conductor 422 is further extended over the left outer back contacts of relay 300, conductor 2 I6, back contacts of relay 300, winding of relay 3!! to battery. Relay 3H operates and closes an obvious circuit for relay 3I2 which also operates. Relay 309 is polarized, is without a biasing spring and its armature may therefore be either on its front or back contact or between the two. If it is neither on its back contact or front contact at the time the line observing circuit is locked to the trunk then ground on conductor 2I6 is extended through the back contacts of relay 3I2 over the following parallel paths: (1) through the left back contacts of re- Relays 200,

lay 3!2, secondary winding (S) of relay 309, middle contacts of jack 3 5, resistance 3 l6, resistance 322 to battery; (2) through the left back contacts of relay 3!?2, primary winding (P) of relay 309, top contacts of jack 3l5, condenser 320, resistance 322 to battery; (3) through the left back contacts of relay 3l2, bottom contacts of jack 3l5, resistance 3!? to battery. The closure of the above circuits serves to place the polarized relay 303 on its back contact as soon as the charging current of condenser 320 has died down. If, on the other hand, the armature of relay 303 is in its front contact initially, then the grounding of conductor 2!3 establishes an immediate circuit for relay 320 which operates at this time and releases as soon as relay 333 breaks its front contact as a result of the effects of the three circuits described above. As soon as the armature of relay 333 makes its back contact, relay 3!! operates, in turn operating relay 3 2 as described. Relay 3!? closes a circuit for relay extending from ground on conductor 2|6, right front contacts of relay 3l2, left normally made contacts of relay 338, winding of relay 333 to battery. Relay 3l2 on its left front contacts further closes the charging circuit of condenser 323 which, being in series with the primary winding (P) of relay 339, the charging current flowing through said winding causes the operation of said relay as the current flow is now in the proper direction for operation. Relay 338 operated locks over its left outer contacts to ground on conductor 2l3, closes a path extending from ground on the right front contacts of relay 3 l 2, left inner contacts of relay 338, left normal contacts of relay 30!, winding of relay 33!, resistance 3l8 to battery. Relay 33! operates. Prior to the operation of relay 33!, however, the same ground is extended to both sides of the winding of relay 333 as follows: to one side by way of the left normal contacts of relay 30! and supplemented after its operation by ground on conductor 253 through its left front contacts, while to its other side the ground on conductor 2H5 is extended over the right outer back contact of relay 333, to the winding thereof. Relay 303 being thus short circuited, does not operate at this time. Relay 333 further closes a supplementary holding path for relay 3H from ground on conductor 2 !3 over V its right outer contacts and normal contacts of relay 310 to the winding of relay 3! Relay 303 operated, operates relay 3l3 and opens the above described supplementary path which holds relay 3!! thereby releasing this relay which, in turn, releases relay 3!2. The release of relay 3E2 closes a supplementary path from ground on conductor 2 I3 to hold relay 3!!! operated should relay 333 prematurely release and removes the shunt around the winding of relay 303 which now operates and locks to conductor 2l3 in parallel with relay 302 extending from ground on its left inner contacts, left outer back contacts of relay 332, winding of relay 302, resistance 3I3 to battery. Relay 332 operates and short circuits relay 334 by extending ground on conductor 2 3 over its left outer front contacts to the winding of relay 304. Relay 334, therefore, does not operate at this time. Relay 3l2 released, again connects ground from conductor 2l3 through its left back contacts to the windings of relay 333 and to condenser 323 in such a direction as to place the relay on its back contact as soon as the charging current of condenser 323 has died down. Relay 303 released, again operates relays 3!! and M2 as before, which latter relay, on operating, connects ground on conductor 2|6 over its left front contact in preparation of previously described circuits for reoperating relay 333 and, through its right front contacts, again connects ground to the left inner contacts of relay 308, and shunts and. causes the release of relay 30! over the left inner make contacts of relay 303.

When relay 309 operates again, it causes the operation of relay 3!3 which again releases relays 3! l and M2, the latter in turn holding relay 3l0 operated and opening the circuit of relay 303 which releases. Relay 303 released, removes the shunt from the winding of relay 333 which op-.

crates in a circuit from battery through resistance 323, winding of relay 304, left outer front.

contacts of relay 332, to ground on conductor 2!3. Relay 354 operated closes a circuit from ground on its right outer contacts, left inner back contacts of relay 305, winding of relay 3M to battery. Relay 3I4 operates. Relay 3l2, when released, again closes the above described circuits to place relay 333 on its back contact. At the end of two complete cycles of operation and release of relay 303 and the corresponding release and operation of relay 3H2, relays 30! and 303 have operated and released and, in turn, caused the operation and locking of relays 332 and 304, the latter further closing the circuit of relay 3M as already described. A third cycle of operations will cause the reoperation of relays 30! and 333 in the sequence described except that, when the relay 333 reoperates on the third cycle, a shunt circuit for relay 332 is established from ground on the left inner contacts of relay 303, left inner front contacts of relay 304 to resistance 3l9. Relay 332 releases but relay 333 now holds over a circuit from ground on the left inner contacts of relay 333, left outer normal contacts of relay 332 to the winding of relay 334. At the end of the fourth cycle, relay 333 releases which, in turn, opens the above holding circuit for relay 304 which also releases. The short circuit around the winding of relay 305 is now removed and this relay operates in the locking winding of relay 3M.

The results of the four cycles of operation above described may be recapitulated as follows:

Relay 3!! operated-operates relay 33! Relay 3l2 releasedoperates relay 303, operates relay 302 Relay 3l2 operatedreleases relay 30! Relay 312 releasedreleases relay 333, operates relay 304, operates relay 3M Relay 3H2 operated-operates relay 33! Relay 3 l 2 releasedoperates relay 333, releases Relay 3l2 operatcdre1eases relay 33! Relay 3!2 releasedreleases relay 303, releases 3514, operates relay 305.

Although the above pulsing circuit has been described in detail for the better understanding of the present invention, the same pulsing circuit is more completely described in the above mentioned patent to Clark.

At the end of four cycles, therefore, relays 30!, 333. 332 and 304 are normal and relays 305 and 3M are operated. Relay 3! upon operating at the end of the second cycle closes a circuit to operate relay 53! which circuit extends from battery through the winding of relay 50!, conductor 503, left contacts of relay 3! to ground, while relay 335 closes conductors 333 and 434 of the outgoing trunk to the central observing bureau over a loop extending from conductor 433, right front contacts of relay 50I, conductor 509, right outer back contacts of relay 305, which is normal at the end of the second cycle, conductor 5I0, left front contacts of relay 50I to conductor 434.

When relay 303 operates at the end of the third cycle, ground is connected to conductors 433 and 434 from the right inner contacts of relay 303. This condition is maintained until relay 303 is released and relay 305 operated, both of which events occur at the termination of the fourth cycle and at which, time conductor 433 is disconnected from conductor 434 and ground is removed from both, conductor 433 (conductor 509) now being extended over the right outer front contacts of relay 305 to the left front contact of relay 3I0 and conductor 434 (conductor 5I0) being extended over the right inner front contact of relay 305 to the right contact of relay 3I I. Both of these conductors are controlled in this manner to discharge the capacity of the conductors prior to the transmission of impulses to the service observing position so as to prevent the false operation of the impulse relays at the'central position as more fully described hereinafter.

Relay 305 operated, locks in series with relay 3I4 to ground over the right contacts of relay 3I4. When, now, relay 3 operates again on the release of relay 309 at the beginning of the fifth cycle, a circuit is closed from ground on its left contacts, left outer contacts of relay 305, normal contacts of relay 3I3, winding of relay 3I3 to battery. Relay 3I3 operates and locks 'to ground on conductor 2I6 over its left front contacts and performs functions to be noted hereinafter. The purpose of the delay measured by four cycles of operation of relay 309 before transmitting impulses which designate the arbitrary number of the observing line is to insure sufficient time for the trunk to be locked to an operators position at the central observing bureau and to insure, further, that the position circuit is prepared to receive the impulses as well so as to enable the calling line circuit to be released in case the trunk is unable to lock itself to an observers position.

At the end of the first four cycles of the pulsing circuit above described another group of four is started immediately thereafter to produce eight call indicator impulses. These impulses are used for transmitting a two-digit number from 00 to 99 over conductors 433 and 434 of the trunk to the control and display circuit located at the central observing position and shown as a part thereof in Fig. 8. The path from the contacts of the register relays to the contacts of the steering relays in the display circuit is always closed just one impulse before it is required as described in the above mentioned patent to Clark. That is, a negative impulse path is prepared during the transmission of the preceding positive impulse and a positive impulse path is prepared during the transmission of the preceding negative impulse. The fourth release of relay 3 I2 as already described closes a path to place relay 309 on its back contact and, as soon as this occurs, relay 3 operates which, in turn, operates relay 3I2 as well as relay 3 I3 through the left center front contacts of relay 305 as already described. Relay 3I3 operated, locks to ground on conductor 2I5 and connects 48-volt battery through high resistance 32I to conductor 5I0 and thence to conductor 434 of the trunk and through low resistance 2I8 to the armatures of the numerical register relays for digits requiring heavy negative impulses. Battery through high resistance 2|! is permanently connected to the armatures of said register relays for digits requiring light positive impulses. The contacts of the register relays in Fig. 2 are wired to those of relays 30l,

303, 302, and 304 in such a manner that the required battery condition may be placed on conductor 433 or 434 of the trunk at the proper time to transmit the impulses required for the particular tens and units digits as determined by 10 the register relays operated. In order to prevent the possible opening of conductors 433 and 434 between impulses and to prevent surges due to cable capacity from disturbing pulsing conditions, direct ground is connected to both con- 15' ductors during the releasing time of relay 3 at the end of a positive impulse and during the operating time of relay 3I2 and the releasing time of relay 3I0 at the end of a negative impulse. Relays 309, 3I I, and 3I2 continue to actuate relays 2'0 30l, 303, 302, and 304 as already described, a. positive or blank impulse being transmitted when relay 3 I 2 is operated and a negative impulse when said relay is released.

As described in the above mentioned patent 5 to Clark, the code impulses are either (1) light negative, (2) heavy negative, (3) light positive or (4) a blank. Since the impulsecode for numbers assigned for arbitrary identification of the observing line circuit is the same as that used 30 for called subscribers numbers as shown in said Clark patent, and since it has been assumed that the number assigned to the line observing circuit A herein used for illustration is 17 the impulse code of the four impulses for the tens 5 digit 1 is (1) positive, (2) light negative, (3) blank, (4) light negative, while the impulse code of the four impulses for the units digit 7 is (1) blank, (2) heavy negative, (3) blank, (4) heavy negative. Consequently, when the pulsing loop 40 is closed at the beginning of the fifth pulsing cycle with the operation of relay 30l, a circuit is completed from battery through resistance 2I I, contacts of relay 200, left inner back contacts of relay 302, left outer back contacts of relay 303, 45 right outer front contacts of relay 305, conductor 509, right front contacts of relay 50I, conductor 433, left inner front contacts of relay I08, conductor 920, right back contacts of relay 9 I 9, winding of relay I, winding of relay 800, winding 50 of relay 802, left outer back contacts of relay 9| 9, conductor 933, left outer front contacts of relay I08, conductor 434, left front contacts of relay 50I, conductor 5I0, right inner front contacts of relay 305 to ground on the right contacts 55 of relay 3I I. Relays 80I, 800 and 002 are the impulsing relays and respond, respectively, to positive, negative and heavy negative impulses, all in accordance with the above mentioned patent to Clark. 0

The first impulse, according to the code, is positive and the polarity of the above described circuit with respect to relay 80I is likewise positive so that relay 80I operates. Accordingly, a circuit is completed from ground on conductor 66 903, normal contacts of relay 922, conductor 934, contacts of relay 80I right back contacts of relay 804, right back contacts of relay 806, right winding of relay 8I2 to battery. Relay 8I2 operates and locks in a circuit from.- battery through its 70 left winding and left inner contacts, conductor 934, to ground.

The next impulse is a light negative and is transmitted at the end of the fifth cycle, that is, with relays 30l, 302 and 303 operated, and relays 3" and 3I2 released. Consequently, a circuit is completed from battery on the right contacts of relay 313, high resistance 321, right inner contacts of relay 305, conductor 5E0, through the previously described trunk loop back to conductor 509, right outer front contacts of relay 305 to ground on the left contacts of relay 310. The direction of current flow is now opposite to that of the first pulse above described and causes the operation of relay 800 which then closes a circuit extending from ground on conductor 934, contacts of relay 800,1ft normal contacts and winding of relay 804, resistance 811 to battery. Relay 804 Operates. Relay 803, however, is short circuited by the operating ground above traced and also from ground through the left normal contacts of relay 804 to the same ground through the contacts of relay 800, and through the left front contacts of relay 804 when this relay operates.

The next impulse, in the sixth cycle, is a blank, causing thereby a release of relay 800 which, in turn, causes a removal of the short circuit around relay 803 thereby causing this relay to operate in parallel with relay 804 from the ground extended through the left front contacts of relay 804.

The next impulse transmitted at the end of thesixth impulsing cycle is a light negative, has the same circuit path as the second impulse and likewise causes the operation of relay 800. A short circuiting path for relay B04 is now completed from ground through the contacts of relay 800, left front contacts of relay 803, to the lower side of the winding of relay 804. Relay 804 releases but relay 803 is prevented from releasing by the presence of the ground on the contacts of relay 800 through the continuity normal contacts of relay 804. Relay 803, therefore, locally holds to the contacts of relay 000 for the duration of the impulse and, when this is terminated, relay 800 releases, in turn, causing the release of relay 803.

At the end of the sixth cycle, relay 302 and 304 remain operated and cause a circuit to be completed from battery through the winding of relay 306, left inner front contacts of relay 305, right outer contacts of relay 304 to ground. Relay 300 operates, and closes a locking path through the winding of relay 301 and its own front contact to ground on conductor 2I6. Relay 301, however, does not operate at this time as the operating ground for relay 300 holds it short circuited.

The sending of the four impulses comprising the code of the tens digit of the arbitrary number assigned to the calling line, therefore, results in the operationand locking of relay 812. At the beginning of the third impulse, however, that is, at the instant relay 803 operates, a circuit is closed from battery through the winding of relay 806, right inner back contacts of relay 805, right inner front contacts of relay 803, to ground over conductor 93.4. Relay 800 operates and closes a locking circuit for itself through the winding of relay 805, left contacts of relay 800 to ground on conductor 934. Relay 805, however, is prevented from operating in this locking circuit by the connection of short circuiting ground to both sides of its winding, one of which grounds is traced above to the winding of relay 800 and is controlled through the contacts of relay 803. At the end of the last impulse, when relay 803 releases, this short circuiting ground is removed and relay 805 operates in the locking circuit of relay 806 as above traced.

The second group of impulses are those which comprise the code for the digit 1 and consists of a first blank impulse, a second heavy negative pulse, a third blank impulse and a fourth heavy negative impulse. The blank impulse is transr5 mitted during the first impulse operation of the seventh impulse cycle. The closure of the circuit for the heavy negative impulse, which is transmitted during the second impulse of the seventh impulse cycle, completes a path from 10; ground on the left contacts of relay 3), right outer front contacts of relay 305, conductor 509, overthe trunk loop as previously described, conductor 5I0, right inner front contacts of relay 305, right front contacts of relay 30l, left outer m front contacts of relay 304, contacts of relay 2| l, low resistance 2 l8, battery through the front contacts of relay 313. This circuit causes the operation of relays 800 and 802. Relay operates and causes the operation of relay 804 as above described while relay 802 completes a circuit from ground on conductor 934, contacts of relay'802, right back contacts of relay 803, left inner front contacts of relay 805, winding of relay 809, to 251 battery. Relay 809 operates and locks in a circuit from battery through its left winding and contacts, to ground on conductor 934. The termination of the impulse causes the operation of relay 803 in series with relay 804, which results 30 1 in the closure of a circuit from battery through the winding of relay 801, right inner front contacts of relay 805, right inner front contacts of relay 003, to ground on conductor 934. Relay 801 operates and closes a circuit through its winding, winding of relay 9l9, contacts of relay 801, to ground on the right inner contacts of relay 108 to perform functions hereinafter described. Relay 9l9 being shunted does not operate at this time. 4.0

The transmission of the fourth and heavy negative impulse, which is transmitted during the fourth impulse of the eighth impulse cycle, completes a path from ground on the left front contacts of relay 3|0, right outer front contacts of 45 relay 305, conductor 509, over the trunk loop as previously described, conductor 510, right inner front contacts of relay 305, right back contacts of relay 30l, right normal contacts of relay 302, contacts of relay 214, low resistance 218, contacts 50 of relay 3 I 3, to battery. This circuit again causes the operation of relays 000 and 802, the former causing the release of relay 804 and the latter the closure of a circuit from ground on conductor 934, right outer front contacts of relay 803, right outer front contacts of relay 805, left winding of relay 8H to battery. Relay 8 operates and locks in a circuit from battery through its right winding and right inner contacts to ground on 60 conductor 934. At the termination of this last impulse, relays 800 and 802 both release, relay 800 causing the release of relay 803. The shunt around the winding of relay M9 is now opened and relay 919 operates in the locking circuit of 65 I relay 801. With the termination of the last impulse, and the consequent release of relay 304, the shunt around the winding of relay 301 is removed and this relay now operates in series with relay 300 to perform functions hereinafter described. 7 The impulse code having been transmitted and the proper register relays operated and locked in response thereto a lamp circuit is closed with the operation of relay 9 I 9 which extends from battery through the No. 1 tens lamp 8|9, left outer front 7 relays release.

- contacts of relay 8! l right outer back contacts of relay 808, right front contacts of relay 860, to ground on conductor 935, as previously traced. This circuit causes the units lamp 820 to glow which, in combination with the tens lamp, displays to the operator the arbitrary number 17 of the calling line on which service observations are being made, and is maintained glowing steadily until the operator releases the call.

After the transmission of the final impulse, relay 301 operates as already described. On the next operation of relay 3, a circuit is closed for operating relay 300 extending from ground on the left contacts of relay 3! I, left outer contacts oi relay 305, contacts of relay 381, left inner back contacts of relay 300, Winding of relay 300, to battery. Relay 309 operated, opens the holding circuit for the register, steering and impulser relays including that of relay 50!. All of these The operation of relay 300 and the release of relay 50! extend battery through the winding of relay 4H3, right outer contacts of relay 300, right back contacts of relay 5!]! to conductor 433 to aid in permitting the operator at the distant end to release the trunk as described hereinafter. The operation of relay 300 further opens its right back contact thus rendering the automatic release feature ineffective and, at its inner right front contact partially prepares the circuit of relay 435 to enable the observing operator to hold an observing line and talk to the subscriber thereon in case of a trouble condition, relay 435 operating in a circuit made efiective when the operator at the observing position operates the position talking key as more completely described hereinafter.

The line indication impulses having been transmitted, the observation position is ready to respond to the next operations of the line under observation which will be generally that of dialing the called subscribers number. Before describing the dial pulsing operations, however, it is desirable to explain somewhat generally the arrangement of the pulse amplifying circuit -which forms a part of the service observation trunk but the combination of which with a service observation trunk, is old in the telephone art and hence not herein described in detail. It comprises, essentially, vacuum tubes 424 and 425 and the polarized differential relay 408. Vacuum 424 is the operating tube and its grid element is connected through leak resistance 426and normal contacts of key MS to conductor H2 of the line and is therefore subjected to the changes of potential that occur on this conductor. The plate circuit of this tube is connected through the normal contacts of jack 431, middle winding (S) of relay 408, normal contacts of both jacks 421 and 428, lamp 429 to positive battery (110V) Vacuum tube 425 is simply a balancing tube for the purpose of compensating for variationsin the positive battery. The grid or" this tube, that is, of tube 424, therefore, is maintained at a constant fixed potential after initial adjustment through the adjusting element 430. The

plate circuit of tube 425 is connected through the normal contacts of jack 428, primary winding P of relay 4%, bottom normal contacts of jack 42! and lamp 429 to positive battery (110V). The right winding (P) and secondary winding (S) of relay 408 are wound diiferentially with respect to each other and have an equal and opposite number of turns. Since relay 408 in this preferred embodiment of our invention does not have a biasing spring for controlling therest position of its armature, the tertiary winding T is provided, and is so wound as to place the relay on its back contact when the right and middle windings are exactly balanced and energized at the same time when winding T is energized. The pulsing circuit is so arranged that there will be equal and opposite number of ampereturns acting through the primary P and secondary S windings of relay 468 when the subscriber or selector loop is open and the voltage on the ring of the line is the absolute minimum.

Before the subscribers dial is moved off-normal, the grid-to-filament potential of tube 424 becomes more positive, resulting in an increase in the plate current through the secondary winding of relay 408. This increase in ampere-turns through the secondary winding overbalances the combined ampere-turns acting through the primary P and tertiary T windings, causing the armature of relay 408 to move to its front contact and prevent the operation of relays 4!2 and 4H3 to the ground connected to the armature of relay 4% by the operation of relay 42! as already described. With relays M2 and M6 normal, the battery and ground closure over the trunk conductors4l4, 4!! to the central observing bureau remains in the proper direction to maintain the polarized relay 104 at the desk end of the trunk in an operated condition. When the dial contacts are opened, the grid-to-filament potential of vacuum tube 424 becomes more negative, re-

sulting in a decrease in the plate current through the secondary winding of relay 408. This decreased current through the secondary winding is overbalanced by the combined current flowing through the primary P and tertiary T windings, and the armature of relay 408 moves to its back contact, thereby causing the operation of relays M2 and .416 in parallel. These relays operated, reverse the battery and ground connections through resistances 4! and H5 respectively and the current flow through the circuit comprising retardation coil 4!3 and relay 104 at the central observing bureau is reversed, thereby causing relay 104 to be released. Relay 104, when it makes its back contacts, closes a circuit from ground through its back contacts, right inner contacts of relay 100, right outer contacts of relay 602, winding of relay 9l0, normal contacts of relay 9! l, winding of pen register magnet 9! 2, resistance 9! 3 to battery. The pen register operates in the well known manner and records a dash on the pen register tape. Relay 408 thus operates and releases, in turn operating and releasing relays M2 and M6 for each pulse sent out from the subscribers dial in response to which the battery and ground are alternately connected to conductors 4!! and 4! 4 of the trunk to the central observing bureau to operate and release relay 104 which, in turn, actuates the pen register 9|3 to record the pulses on the cooperating moving tape.

When relay 104 is released for a sufllcient period of time, that is, after the reception of all the impulses of a digit, relay 9H3 remains on its front contacts long enough to operate relay 914 which, on operating, extends an operating circuit from ground on the left contacts of relay 910, to relay M5 while this last relay, on operating, extends the ground which closed the circuit of relay sue through its own front contacts to the winding of relay 9! l which operates. Relay 9H locks under control of relays 852 and Lid. When relay Hi l is reoperated, relay 95! is released and the same cycle of operations is repeated for each series of impulses, said impulses being registered on a moving tape actuated by the mechanism (not shown) of which magnet 9l2 forms a part.

The restoring of the subscribers receiver has the same effect as opening the dial contacts. As soon as the line relay in the sender is again placed across the line, relay 4B8 releases and causes the reoperation of relay M2 and die, thereby ultimately causing the pen register to record the subscribers disconnection.

Condenser B48 is connected between the grid and negative filament terminal of vacuum tube 424 in order to prevent the registration of split impulses when observing on step-by-step pay station lines as well as on subscribers lines having maximum sub-set capacity. The battery through resistance 432 connected to the front contact of relay 308 and to condenser 33! is for the purpose of providing for satisfactory recording of impulses when observing on panel lines having maximum sub-set capacity and fast dials. When the front contact of relay 468 breaks, the charge on condenser 413i is increased which causes a current surge through the primary winding of relay 408 which aids in placing the armature of the relay on its back contact.

Immediately after the line indication numbers have been transmitted, the observation operators circuit is placed in a talking and listening condition with respect to the calling subscriber. For this purpose, a single stage vacuum tube amplifler M is provided in monitoring over a subscribers connection and it also serves as a oneway repeater to prevent noise transference to the circuit that is under observation. At all times when a call is locked into a position, however, the service observer may hear in her headset any conversation or tones taking place on the subscribers line.

If the operator has occasion to talk to the subscriber, key SZI is operated. A circuit is now closed from ground on the left contacts of key 92I to the winding of relay 9% which, on operating, closes a circuit extending from battery through the winding of relay 323, left outer contacts of relay 935, transmitter 925, right outer front contacts of relay Q36, right front contacts of talking key 92!, secondary winding of induction coil 956, to ground. Key 532i also closes a circuit from ground on the left inner contacts of talking key 92!, upper winding of retardation coil 9 l '1, front contacts of relay 9 i 9, conductor 933, left outer front contacts of relay i133, conductor 434, left back contacts of relay :33 to the winding of relay 5%, operating this relay. Relay 586 operated closes a circuit extending from ground through the contacts of relay 5%, conductor 502, right inner front contacts of relay 360, winding of relay 35 to battery. Relay 335 operated places a holding bridge consisting of. windings 431 and 438 of repeating cell @353 in series extending from winding 538, top outer contacts of relay 435, conductor HI, over the subscribers line or central office loop, conductor l H,

bottom outer contacts of relay 435, winding 431, resistance 446. This loop across the line conductors prevents the central oflice apparatus from releasing even though the subscriber restores his receiver to the switchhook. The operation of relay 435 also closes an obvious circuit for relay 444 which operates and closes the talking conductors through to the windings M5 and 446 of repeating coil 436 to the central observing position thereby providing a twoway transmission circuit to'enable the observing operator to converse with the subscriber. It must be noted, however, that the observing operator is unable to hold a subscribers line or talk to the subscriber until the call indicator impulses for line identification have been transmitted as previously indicated since the circuit for relay Q35 can not be completed until relay 398 operates, which occurs after the transmission of the line indicating impulses as already described. Relay 435 is made slow to operate in order to prevent its false operation during short closures of the contacts of relay 5% should this relay respond to line surges.

Should the observing operator, in noticing some service irregularity, desire to communicate with a switchman of the ofiice of the subscribers line, key 925 is operated. The circuit for relay 936 is now closed from ground on the left outer contacts of. key 925 and the operation of relay 936 closes a previously described circuit for relay 823 Further, the handset receiver 826 is connected over the inner front contacts of said key to induction coil 9H. Key 925 also closes an obvious circuit for relay 821 which, in turn, opcrates relay 933. A circuit is now closed from ground over the left outer contacts of relay 921, right contacts of relay 93%, lower winding of retardation coil 91?, right front contact of relay 959, conductor 929, left inner front contacts of relay H38, conductor 433, right back contacts of relay bill, right outer front contacts of relay 3&9, winding of relay M8 to battery. Relay M8 operates and closes a circuit extending from ground on its contacts, top inner front contacts of relay 435, conductor M5, winding of relay 5! I to battery. Relay 5 operates and connects battery to sleeve conductor 512 of a tie line to the chief switchmans desk. This battery closure operates a relay, which in turn, lights a lamp at the chief switchmans desk who answers the call and converses with the operator at the central observing position through repeating coil 5 I 3 connected to the trunk over conductors 333 and 334 through the back contacts of relay 56 I If, at this time talking key 929 is operated, the switchmans talking circuit is held but it further allows the operator to talk to the subscriber.

When coin collect current is connected to the subscribers line, relay 259 operates, in turn operating relay 220 in a circuit extending from ground through its front contacts, back contacts of relay 22!, left winding of relay 229 to battery. Relay 228 operates, opens the path to the winding of relay Hi and connects low tone circuit'LT over its left contacts, conductor 222, winding 44! of output transformer 335 to ground. This tone is now transmitted to the operator at the central observing bureau over a previously described circuit to indicate that the coin has been collected. The operation of relay 220 also closes its locking winding through its front contacts to the front contacts of relay 223 in order to prevent relay 220 from releasing until both relays 219 and 223 are normal. This arrangement is provided to prevent the transmission of both a coin collect and coin 

